In television recording by way of a color camera or color film scanning, there have been numerous improvements in an attempt to obtain clearer and more sharply defined picture. What has resulted however is cross color interference particularly in the operating range of conventional color television signal coding such as that provided by NTSC and PAL, for example. Cross color is interference in a color television's receiver chrominance channel caused by cross talk from the monochrome signals. In other words the black and white information crosses over into the frequency range of the color channels, which results in, for example, striped or fine patterned movable video surfaces particularly flat surfaces (i.e., suits and ties of actors etc), causing an undesirable color appearance.
In an attempt to eliminate such interference, a band elimination filter in the band carrier range or a corresponding low pass filter in the luminance (brightness) channel of the coders of the video color cameras has been heretofore utilized however a problem with such an arrangement is that it permanently deteriorates the video picture.
Another improvement to the video quality involved suppressing the amplitude of the interfering luminance components as described in German Patent Ser. No. DE-AS 2411296. To accomplish this, the luminance signal is fed to a time delay member or circuit as well as a band pass filter. The output signal of the band pass filter is then subtracted from the output signal of the time delay circuit to provide for the appropriate suppression.
In order to partially correct the deterioration of the video picture caused thereby, the output signal of the band pass filter is further limited and added to the output signal. However, the color video signal is not sufficient with respect to sharpness or with respect to the interference suppression. In addition, it might be noted that such a device operates not only with respect to, for example, flat appearing objects in the picture which generate frequencies in the color carrier range of the luminance signal, but also affects steep picture transmission (steep signal rise or drop, i.e. black-white jump) and thereby reduces the steepness in the signal rise, thereby having an undesirous effect on the picture.
Regarding the use of SECAM color signal coders, there is described in German Pat. No. DE-OS 14 37 744 a means to control the amplitude and phase of the color carrier depending on the cross color error to be expected. However, this results in only a portion of the cross color interference being suppressed. Further, this principle can not possible be used with
coders.
There is presently known a circuit for detecting and if necessary suppressing cross over interferences from the luminance (brightness) channel into the color channel of a color video transmission device as for example that described in German Pat. No. DE-AS 28 21 183. In this device there is provided a time delay member or circuit and a luminance filter which is switchable by means of the control signal into the luminance channel. For storing a video line, there is provided a series circuit fed with the luminance signal consisting of a band pass filter synchronized to the color carrier. An integrator is provided which is synchronized to the width of the picture element of the signal source with the time delay circuit storing a video field. A logic member is provided and arranged in such a manner that the logic member only switches through when it is over a predetermined amount (N) of successive lines of the luminance signal when color carrier frequency luminance portions are present. In the switched through condition, the output signal of the logic member represents the control signal, which if necessary, controls a reverse switch for switching on the filter. Alternatively, the logic member switches the time delay member to the luminance channel.
However, this circuit suffers the disadvantages that aside from being relatively complicated and expensive, over a plurality of video fields a determination is made whether cross color conditions are present, and if present limits the luminance signal in the band width for the total picture and not just for parts of the picture where the cross colors appear.
Accordingly, a need exists for a relatively simple yet effective means to control cross color which is relatively inexpensive and avoids the disadvantages of the circuits aforenoted.